In general, a power distribution system is composed of a high-voltage system (e.g., 3300 volts to 6600 volts) and a low voltage system (e.g., 100 volts to 200 volts). A power receiving end of a general consumer is connected to the low voltage system. A power company is obliged to maintain voltage at the power receiving end of the general consumer within a proper range (e.g., in the case of power reception of 100 volts, maintain the voltage at 95 volts to 107 volts). Therefore, the power company maintains voltage at the power receiving end of the general consumer by adjusting a control amount of a power control apparatus (e.g., an LRT (Load Ratio control Transformer) or an SVR (Step Voltage Regulator)) connected to the high-voltage system. Note that the voltage of the voltage control apparatus is controlled by a voltage controller integrated with or in parallel with the voltage control apparatus, for example.
The voltage control apparatus of a transformer type such as the LRT or the SVR has an object of keeping the voltage at all points on a load side within a proper range by changing the voltage on the load side according to tap operation based on LDC (Line Drop Compensator) control. The LDC control calculates, on the basis of voltage/current information measured by the voltage control apparatus and on the estimate that a load of a power distribution line is larger and the voltage at the end of the power distribution line is lower as an electric current is larger, a reasonable load side voltage for keeping the voltage at all the points on the load side within the proper range.
Incidentally, the LDC control is configured on the premise that a load distribution of the power distribution system equally changes, that is, the voltage at respective points of the power distribution system change in the same direction. However, in recent years, according to the diversification of use of electricity and the spread of distributed power supplies by solar power generation or the like, the load distribution of the power distribution system tends to greatly fluctuate according to elapse of time. Therefore, it is difficult to estimate a voltage state of the entire power distribution system only from the voltage/current information measured by the voltage control apparatus, and a problem arises in maintaining a proper voltage.
Therefore, a mechanism has been developed in which measurement information of voltage/electric current at respective points of a power distribution system is gathered in a central device (a centralized voltage controller) via a communication network and collectively grasped and the centralized voltage controller instructs a voltage controller about a target voltage (see, for example, Patent Literature 1).
Note that, to prevent wear of the apparatus, in general, the voltage control apparatus of the transformer type keeps the number of tap changes below 30 taps per one day in average.
To cope with sudden fluctuation in voltage accompanying change of a solar power generation amount due to a flow of cloud, application of a voltage control apparatus of a reactive power adjustment type such as an SVC (Static Var Compensator) or a power conditioning system (hereinafter referred to as PCS) to a power generation system also has been examined. Concerning the voltage control apparatus of the reactive power adjustment type, costs and setting places increase when a capacity (VA) is increased, and thus it alone is not suitable for coping with large voltage fluctuation in the power distribution system and a basic way of use thereof is absorption of voltage fluctuation in units of second.
However, even if a capacity is small, it is expected to cope with large voltage fluctuation in time order equal to or longer than 1 minute by causing a plurality of the voltage control apparatuses of the reactive power adjustment type to operate in cooperation with one another from the centralized voltage controller. For example, if PCSs are essential for solar power generation, it is also expected that utilizing such cooperative control among the PCSs eliminates the need to take an additional measure against the voltage problem such as setting of another SVC.
In this way, in a situation in which a plurality of voltage control apparatuses are set on one power distribution line, to realize a cooperative operation among the voltage control apparatuses, it is expected to develop a mechanism for grasping a voltage state of the entire power distribution system with the centralized voltage controller and sending an appropriate command to the voltage controllers and apply the mechanism to the power distribution system.